delta

Delta is a term with several distinct meanings across geography, mathematics, aviation, biology, and finance. In geography, a delta is a landform at the mouth of a river where sediment deposits create a triangular or fan-shaped plain. The term is exemplified by the Nile and Mississippi deltas, though deltas vary in shape and size depending on sediment supply and flow. The name derives from the Greek letter delta (Δ, δ), which historically resembled a triangle.

In mathematics and science, delta denotes change or difference. The uppercase Delta (Δ) is commonly used to indicate a difference between two values (for example, Δx is the change in x). The lowercase delta (δ) has other uses, such as small changes or uncertainty, and the Dirac delta is a distribution used in physics and engineering.

Delta Airlines is a major American airline based in Atlanta, Georgia, and a member of the SkyTeam alliance. It operates an extensive domestic and international network and traces its origins to 1924 as Huff Daland Dusters.

Delta is also used in virology to name the SARS-CoV-2 variant B.1.617.2, designated by the World Health Organization as the Delta variant after being first detected in India in 2020 and recognized as a variant of concern in 2021; it became a dominant strain in many regions.

In finance, the delta of an option measures its sensitivity to changes in the price of the underlying asset.

Etymologically, delta stems from the Greek letter delta, which itself means "triangle" and is the fourth letter of the Greek alphabet.